The present invention relates generally to numerically controlled machines, and more particularly to a contour compensation method for numerically controlled machines.
In the case of numerically controlled machines, for example numerical machine tools or robots, the trajectory curve on which a tool is guided is subdivided into path segments. This is accomplished by calculating interpolation points along the trajectory curve, which interpolation points are successively traversed by the machine tool's guide device. It is usually very time-consuming to calculate the interpolation points for a specified trajectory curve. Therefore, in many cases, this is carried out off-line before the first machining operation. The calculated interpolation points can then be stored and transmitted during the operation of the specific numerically controlled machine directly to its position control loop, whereupon a tool is guided along the trajectory curve specified by the interpolation points.
In the machining of tools, it can happen that a change in the tool geometry makes it necessary to alter the trajectory curve. Thus, for example, the radius of a milling tool can become smaller as the result of wear. Since, when circular tools are used, the tool center point is ordinarily guided along the specified trajectory curve, the clearance of the trajectory curve up to the workpiece contour has to be modified. However, it could also be necessary, for example, to replace a worn-out tool with a new one. In this case, the radius would become enlarged for a circular tool, so that the trajectory curve would have to have a greater clearance to the workpiece contour.
When interpolation points are recalculated at any time because of such changes in the tool geometry, given an unvarying workpiece contour, this leads to considerable machine down-time.
The present invention is directed to the problem of developing a method for achieving a simple path correction for numerically controlled machines, on-line so that machine down time due to recalculation of interpolation points can be eliminated.